1. Field of the Invention
The present invention relates generally to inkjet printing and, in particular, to capping the printhead of an inkjet print cartridge.
2. Related Art
In inkjet printing, one or more print cartridges are inserted in a movable print carriage. Each print cartridge includes a reservoir that holds ink. The ink passes from the reservoir through a multiplicity of nozzles to be ejected from a print cartridge printhead onto a print medium. The print carriage is moved laterally back and forth, and the print medium is advanced past the print carriage to enable printing of a desired image or images on the print medium.
Inkjet print cartridge nozzles commonly become plugged with ink blobs or particulate, or otherwise contaminated with internal bubbles that prevent the nozzles from operating properly, resulting in lower print quality. Consequently, printers and facsimile machines that use inkjet printing typically include a service station that provides for spitting, wiping, capping and priming of each printhead in order to keep the nozzles clean and functioning.
During capping, a cap must be properly aligned with the corresponding printhead. Typically, for inkjet print cartridges, cap alignment must be maintained within a fraction of a millimeter of a nominal value. If the cap is misaligned, the cap can contact one or more of the nozzles and absorb ink from the nozzles through capillary action, dirtying the service station with ink and necessitating priming of the nozzles before printing again. Additionally, improper alignment can cause the cap to inadequately seal the area around the nozzles. As a result, air can enter the area around the printhead, causing the ink to dry out and clog the nozzles. Contaminants may also enter the area around the printhead, eventually causing the nozzles to become clogged.
The cap must also be positioned, in a direction perpendicular to the printhead, so that the cap fits snugly against the printhead to ensure a good seal. However, the cap should not be positioned so that the force applied by the printhead to the cap causes the cap to deform a large amount, since such deformation may result in a poor seal (producing detrimental effects as described above) or may damage the cap or printhead.
Tolerances associated with the manufacture, assembly and operation of an inkjet printing assembly can combine to result in a variation of cap alignment that is too large, or a positioning of the cap (in a direction perpendicular to the printhead) that does not produce a good seal. Such tolerances may also combine to cause positioning of parts of the printing apparatus against each other so that forces build up in parts of the printing apparatus to an unacceptably high level. Such tolerances may be associated with, for instance, positioning of the print cartridge in the corresponding stall of the print carriage, attachment of the print carriage to a print carriage movement mechanism (such as a rod) attached to a printer chassis, assembly of the various components of the service station, and attachment of the service station to the printer chassis.
During wiping, interference between the wiper and the print cartridge must be controlled within a specified dimensional tolerance to achieve the proper wiping force. Typically, for inkjet print cartridges, wiper interference must be maintained within a fraction of a millimeter of a nominal value. If the wiper interference is too small, then the wiping force will be too small and the printhead won't be adequately wiped, resulting in poor print quality and shortened print cartridge life. If the wiper interference is too large, debris will be pushed in to the nozzles, clogging one or more nozzles so that ink cannot be ejected from the nozzle or nozzles, and/or degrading the print quality by partially clogging nozzles or becoming embedded in the ink.
Frequently, the cap and the wiper are mounted on a movable service station sled. For a variety of reasons, there may be a problem with the functionality of the cap, wiper or some other part of the service station sled. For example, because of the frequent contact between the wiper and the print cartridge, the wiper may wear out. Therefore, it is desirable that the service station sled can be replaced without the necessity of replacing the remainder of the service station.
Additionally, printers must include structure for performing various functions, e.g., moving the print carriage, advancing the print medium through a printing path. It is obviously desirable to make the structure for performing these functions as simple, efficient and inexpensive as possible. In particular, it is desirable to use particular components of the printer to perform more than one function, thereby enabling the printer to be made smaller (or, equivalently, perform more functions for the same size), simpler to manufacture and less expensive to manufacture.